Processing of a gas, for example natural gas, synthesis gas, combustion gas, gas from integrated combined cycles, generally involves removal of impurities such as nitrogen (N2), ammonia (NH3), and acid compounds such as carbon dioxide (CO2), hydrogen sulfide (H2S), sulfur dioxide (SO2), COS, CS2 and mercaptans. These impurities are present in various proportions depending on the origin of the gas. In the case of natural gas, CO2 and H2S can be present as traces, some ppm, but they can also represent a quite significant proportion of the raw gas, up to 70% by volume. Other impurities such as COS, CS2 and mercaptans can also be encountered, generally a few thousand ppm.
According to the initial proportions of impurities in the gas to be processed, and also according to the specifications required for the processed gas, various scrubbing processes are used. The most commonly used processes use solvents. These solvents can be of physical or chemical nature. Solvents of physical nature are based on the preferred solubility of the impurities in the solvent, and are therefore favoured by the high partial pressures of the impurities in the gas to be processed. Solvents of chemical nature are ideally used to reach the strictest specifications for the processed gas, by chemical consumption of the species absorbed by reaction with an active agent contained in the absorption solvent. There are also solvents of hybrid nature consisting of a mixture of physical and chemical solvents so as to enjoy the advantages of these two solvents.
Whatever the origin of the gaseous effluent to be processed, the purification loop generally consists of an impurities collection stage using a solvent and of a solvent regeneration stage. The regeneration stage is conditioned by the nature of the solvent used. In the case of a solvent involving a chemical reaction, a thermal regeneration is generally used to obtain a sufficient solvent purity allowing the desired specifications to be reached. Thermal regeneration can be preceded by regeneration by expansion in order to limit the energy required for thermal regeneration. In the case of a solvent of hybrid or physical nature, regeneration is essentially carried out by expansion, possibly completed by a thermal regeneration stage.
The invention proposes improving the regeneration by expansion of a solvent by carrying out an expansion in a two-phase turbine.